"They're revealing information that was frozen into their ancient surfaces. By looking at the surface and how it was modified by the bombardment of meteoroids, we will get an idea of what the early conditions of Ceres and Vesta were and how they changed. So Dawn is a history trip too.

"We're going back in time to the early solar system."

The Dawn spacecraft

Dawn's instruments include a gamma ray and neutron spectrometer that can detect the hydrogen from water.

Evidence of whether water still exists on Ceres could come from frost or vapour on the surface, and possibly liquid water under the surface. The water kept Ceres cool throughout its evolution.

Ceres, named for the Roman goddess of agriculture, revolves around the sun every 4.6 terrestrial years and has an average diameter of approximately 600 miles.

A roughly round object, Ceres orbits the sun in the asteroid belt between Mars and Jupiter, approximately 258 million miles from Earth. Ceres is much larger than Vesta — more than two times further across, with a volume eight or nine times greater — but is less dense, as the material in it is lighter.